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From: Tejun Heo <tj@kernel.org>
To: Shakeel Butt <shakeelb@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux MM <linux-mm@kvack.org>, Kernel Team <kernel-team@fb.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Chris Down <chris@chrisdown.name>,
	Cgroups <cgroups@vger.kernel.org>
Subject: Re: [PATCH 0/3] memcg: Slow down swap allocation as the available space gets depleted
Date: Fri, 17 Apr 2020 12:23:55 -0400	[thread overview]
Message-ID: <20200417162355.GA43469@mtj.thefacebook.com> (raw)
In-Reply-To: <CALvZod78ZUhU+yr2x1h_gv+VgVGTPnSSGKh_+fd+MeiAKreJvg@mail.gmail.com>

Hello,

On Fri, Apr 17, 2020 at 09:11:33AM -0700, Shakeel Butt wrote:
> On Thu, Apr 16, 2020 at 6:06 PM Jakub Kicinski <kuba@kernel.org> wrote:
> >
> > Tejun describes the problem as follows:
> >
> > When swap runs out, there's an abrupt change in system behavior -
> > the anonymous memory suddenly becomes unmanageable which readily
> > breaks any sort of memory isolation and can bring down the whole
> > system.
> 
> Can you please add more info on this abrupt change in system behavior
> and what do you mean by anon memory becoming unmanageable?

In the sense that anonymous memory becomes essentially memlocked.

> Once the system is in global reclaim and doing swapping the memory
> isolation is already broken. Here I am assuming you are talking about

There currently are issues with anonymous memory management which makes them
different / worse than page cache but I don't follow why swapping
necessarily means that isolation is broken. Page refaults don't indicate
that memory isolation is broken after all.

> memcg limit reclaim and memcg limits are overcommitted. Shouldn't
> running out of swap will trigger the OOM earlier which should be
> better than impacting the whole system.

The primary scenario which was being considered was undercommitted
protections but I don't think that makes any relevant differences.

This is exactly similar to delay injection for memory.high. What's desired
is slowing down the workload as the available resource is depleted so that
the resource shortage presents as gradual degradation of performance and
matching increase in resource PSI. This allows the situation to be detected
and handled from userland while avoiding sudden and unpredictable behavior
changes.

Thanks.

-- 
tejun


  reply	other threads:[~2020-04-17 16:24 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-17  1:06 [PATCH 0/3] memcg: Slow down swap allocation as the available space gets depleted Jakub Kicinski
2020-04-17  1:06 ` [PATCH 1/3] mm: prepare for swap over-high accounting and penalty calculation Jakub Kicinski
2020-04-17  1:06 ` [PATCH 2/3] mm: move penalty delay clamping out of calculate_high_delay() Jakub Kicinski
2020-04-17  1:06 ` [PATCH 3/3] mm: automatically penalize tasks with high swap use Jakub Kicinski
2020-04-17  7:37   ` Michal Hocko
2020-04-17 23:22     ` Jakub Kicinski
2020-04-17 16:11 ` [PATCH 0/3] memcg: Slow down swap allocation as the available space gets depleted Shakeel Butt
2020-04-17 16:23   ` Tejun Heo [this message]
2020-04-17 17:18     ` Shakeel Butt
2020-04-17 17:36       ` Tejun Heo
2020-04-17 17:51         ` Shakeel Butt
2020-04-17 19:35           ` Tejun Heo
2020-04-17 21:51             ` Shakeel Butt
2020-04-17 22:59               ` Tejun Heo
2020-04-20 16:12                 ` Shakeel Butt
2020-04-20 16:47                   ` Tejun Heo
2020-04-20 17:03                     ` Michal Hocko
2020-04-20 17:06                       ` Tejun Heo
2020-04-21 11:06                         ` Michal Hocko
2020-04-21 14:27                           ` Johannes Weiner
2020-04-21 16:11                             ` Michal Hocko
2020-04-21 16:56                               ` Johannes Weiner
2020-04-22 13:26                                 ` Michal Hocko
2020-04-22 14:15                                   ` Johannes Weiner
2020-04-22 15:43                                     ` Michal Hocko
2020-04-22 17:13                                       ` Johannes Weiner
2020-04-22 18:49                                         ` Michal Hocko
2020-04-23 15:00                                           ` Johannes Weiner
2020-04-24 15:05                                             ` Michal Hocko
2020-04-28 14:24                                               ` Johannes Weiner
2020-04-29  9:55                                                 ` Michal Hocko
2020-04-21 19:09                             ` Shakeel Butt
2020-04-21 21:59                               ` Johannes Weiner
2020-04-21 22:39                                 ` Shakeel Butt
2020-04-21 15:20                           ` Tejun Heo

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